Almost one in four of the county’s additional population over the past decade were not actually born in Northamptonshire, new figures show.
Analysts at Northamptonshire County Council said the census data released last month shows a gap between the natural population increase and the official figure the census arrived at.
The report said: “Using birth and death data from the 10 years between 2001 and 2011 censuses, we can account for 76 per cent of the total increase in population size, the remainder being due to migration in and out of the county.”
Council statisticians as yet have no idea where the new arrivals have come from.
Data from last year’s census that reveals the country of birth and other information will not be revealed until November. And there is likely to be little information as to where else respondents have lived in the UK.
However, the council’s business intelligence experts said it was likely many of them had come to Northamptonshire to find work or because of a new job.
For example Corby’s male population aged between 25 and 34 and female population aged 25 to 29, people of key working ages, had increased “considerably” .
Elsewhere, South Northamptonshire’s population was significantly smaller than predicted in 2010, with a lower proportion of working age people and children. The report said: “The Office of National Statistics may have overestimated the number of people migrating into the Milton Keynes South Midlands Development.”
The population of Northamptonshire increased by 9.8 per cent between 2001 and 2011 to 691,000, the census showed.
Northamptonshire County Council said the county had 0.7 per cent more people than had previously been estimated in 2010.
Corby had 5,300 more people than previously thought, however South Northamptonshire had 3,500 less.
The total number of households in the county rose by 11.1 per cent.
Under-fives rose by 19 per cent during the decade.
Those in the over-85 age group rose by just under a third.